Question

我有一个包含5720个对象的JSON文件airports.json，我想用Java将文件解析为Objects Airport。下面的代码就是我如何解析它，问题是，它需要花费太多时间来完全解析所有文件，大约1分50秒。

    ArrayList<Airport> arrayAirports = new ArrayList<>();
    String json_response = loadJSONFromAsset();
    try {
        JSONObject airports = new JSONObject(json_response.trim());

        Log.d("Length Array 0", String.valueOf(airports.names().length()));
        Log.d("Length Array 1", String.valueOf(arrayAirports.size()));
        for(int i = 0; i<airports.names().length(); i++){
                JSONObject jsonAirport = airports.getJSONObject(airports.names().getString(i));
                Airport newAirport = new Airport();
                newAirport.name = jsonAirport.getString("name");
                newAirport.city = jsonAirport.getString("city");
                newAirport.country = jsonAirport.getString("country");
                newAirport.latitude = jsonAirport.getString("latitude");
                newAirport.longitude = jsonAirport.getString("longitude");
                newAirport.altitude = jsonAirport.getString("altitude");
                newAirport.iata = jsonAirport.getString("iata");
                newAirport.icao = jsonAirport.getString("icao");
                newAirport.timeZone = jsonAirport.getString("timezone");
                newAirport.dst = jsonAirport.getString("dst");
                arrayAirports.add(newAirport);
        }



    } catch (JSONException e1) {
        e1.printStackTrace();
    }

    Log.d("Length Array 2", String.valueOf(arrayAirports.size()));

有没有办法快速解析它。顺便说一下，我的朋友正在使用Objective C完全解析它。

Link to JSON file

Answer 1

使用GSON代替并用它来衡量速度。虽然有可能只是阅读文件需要很长时间，但整整一分钟似乎都很糟糕。

由于您提到您不知道如何使用GSON，here's a tutorial I wrote for a student on how to use GSON。它假设您从网络调用中获取文件，因此您需要应用它来使用本地JSON文件。

Answer 2

不知道是否对性能有影响，但不应反复拨打names()。在循环之前分配给变量，然后使用它。

JSONArray names = airports.names();
Log.d("Length Array 0", String.valueOf(names.length()));
Log.d("Length Array 1", String.valueOf(arrayAirports.size()));
for(int i = 0; i<names.length(); i++){
    JSONObject jsonAirport = airports.getJSONObject(names.getString(i));
    // code
}

更好的是，使用length()和keys()：

Log.d("Length Array 0", String.valueOf(airports.length()));
Log.d("Length Array 1", String.valueOf(arrayAirports.size()));
for (Iterator<String> nameIter = airports.keys(); nameIter.hasNext(); ){
    String name = nameIter.next();
    JSONObject jsonAirport = airports.getJSONObject(name);
    // code
}

Answer 3

您正在将一个（我猜？）大型JSON数据文件直接放入JSONObject中。

在这种情况下，建议使用基于令牌的阅读器，例如JsonReader。

直接从文档粘贴：

public List readJsonStream(InputStream in ) throws IOException {
    JsonReader reader = new JsonReader(new InputStreamReader( in , "UTF-8"));
    try {
        return readMessagesArray(reader);
        finally {
            reader.close();
        }
    }

    public List readMessagesArray(JsonReader reader) throws IOException {
        List messages = new ArrayList();

        reader.beginArray();
        while (reader.hasNext()) {
            messages.add(readMessage(reader));
        }
        reader.endArray();
        return messages;
    }

    public Message readMessage(JsonReader reader) throws IOException {
        long id = -1;
        String text = null;
        User user = null;
        List geo = null;

        reader.beginObject();
        while (reader.hasNext()) {
            String name = reader.nextName();
            if (name.equals("id")) {
                id = reader.nextLong();
            } else if (name.equals("text")) {
                text = reader.nextString();
            } else if (name.equals("geo") && reader.peek() != JsonToken.NULL) {
                geo = readDoublesArray(reader);
            } else if (name.equals("user")) {
                user = readUser(reader);
            } else {
                reader.skipValue();
            }
        }
        reader.endObject();
        return new Message(id, text, user, geo);
    }

    public List readDoublesArray(JsonReader reader) throws IOException {
        List doubles = new ArrayList();

        reader.beginArray();
        while (reader.hasNext()) {
            doubles.add(reader.nextDouble());
        }
        reader.endArray();
        return doubles;
    }

    public User readUser(JsonReader reader) throws IOException {
        String username = null;
        int followersCount = -1;

        reader.beginObject();
        while (reader.hasNext()) {
            String name = reader.nextName();
            if (name.equals("name")) {
                username = reader.nextString();
            } else if (name.equals("followers_count")) {
                followersCount = reader.nextInt();
            } else {
                reader.skipValue();
            }
        }
        reader.endObject();
        return new User(username, followersCount);
    }
}

JSON解析花费了太多时间 - Android

3 个答案: